When I pay with credit card, it asks for my security code. Where is that located?

For Visa, MasterCard, and Discover: Look at the back of your credit card. You should see a series of numbers adjacent to the signature strip. Your security code(or the "CVV2 Number") is the final three digits.

For American Express: Look at the front of your card. Your security code is the four-digit number located above and to the right of the card number.